A proton and C13 nmr investigation of a number of physical and chemical properties of paramagnetic model heme complexes relevant to the biological role of these complexes as prosthetic groups in hemoproteins is planned. The effect of peripheral substituents as well as axial imidazole bonding on the heme electronic asymmetry will then be characterized using the spread of the individually assigned methyl contact shifts, and this data compared to similar data on hemoproteins. The changes in pi bonding to axial imidazoles as a function of variable trans ligands will be elucidated. The role of heme pi contacts with aromatic pi donors/acceptors in modulating the affinity for, and lability of axially coordinated substrates will be characterized. The detailed analyses of systematic perturbations on the nmr spectra of model complexes are expected to provide a detailed understanding of the hyperfine shifts in hemoproteins in terms of the electronic structure of the iron and protein conformation near the heme pocket. The general utility of proton nmr spectra for investigating structure-function relationships in high-spin myoglobins will be explored.